Transcript Lecture1cdw
NATS 101 Lecture 1 Atmospheric Composition 100 km 100 km C = 2pa 4.084 x 104 km Ratio: Height/ Length is 100/(4.084 x 104) 2.45 x 10-3 - height of the atmosphere is extremely small compared with its length air motions are primarily horizontal. a 6500 km air motions are primarily horizontal very small vertical motions are very important, e.g., they causing the development/inhibition of clouds. Here are some of the characteristic features on thunderstorms. The flat top forms when the updraft encounters the bottom of the stratosphere Some of the weather hazards associated with thunderstorms are heavy rain and flooding, strong winds, and lightning Composition of the atmosphere 1. Permanent gases 2. Variable gases 3. Aerosols 1. Permanent gases stable concentration in the atmosphere. • account for about 99% of the atmospheric mass • occur in a constant proportion in the lowest ~80 km of the atmosphere. • although individual molecules exchange between the atmosphere and Earth, the total concentration remains the same chemical homogeneity • Lowest 80 km is called the Homosphere and is sometimes considered to be the entire atmosphere. • The atmosphere above this is called the Heterosphere. Fill in the blank above with nitrogen 1. Permanent gases N2 + O2 = 99% of atmospheric volume below 80 km. They are chemically active. Ar, Ne, He, Xe < 1% and are chemically inert. ** The residence time of a gas is the average time an individual molecule remains in the atmosphere. This is a list of the 5 most abundant gases in air It includes permanent gases and a couple of the variable gases 1. Permanent gases Nitrogen: • N2 is added and removed from the atmosphere very slowly – long residence time** of ~42 million years. • N2 is relatively unimportant for most meteorological and climate processes • some gases containing N are important to the Earth’s climate such as NO2. Oxygen: • O2 is crucial to the existence of almost all forms of life currently on the Earth. Its residence time is ~5000 years. Most of the oxygen in air comes from plants (photosynthesis) 2. Variable gases distributions vary both in time and space. • account for < 1% of the atmosphere below 80 km. • some of these gases impact the behavior of the atmosphere considerably. H2O + CO2 + O3 = 0.296% of atmospheric volume. Water Vapor (0.25%) • water vapor varies considerably in both space and time. • Continually cycled between atmosphere and earth by evaporation, condensation and precipitation. (hydrologic cycle) • Stores and releases large amounts of heat via evaporation and condensation. • Water vapor has a residence time of only 10 days. • WV density is greatest at the surface, and decreases rapidly with height. • WV is extremely important for clouds • WV absorbs radiant energy emitted from the Earth’s surface. (Greenhouse gas) I don’t think I mentioned this in class on Tuesday. I’ll come back to it briefly on Thursday Carbon Dioxide (0.036%) • (CO2) is supplied to the atmosphere through plant and animal respiration, through decay of organic material, volcanic eruptions, and both natural and anthropogenic (human caused) combustion. • It is removed through photosynthesis, the process by which green plants convert light energy to chemical energy. Oxygen is released into the atmosphere as a by-product. • CO2 has a residence time of ~150 yrs. • It is an effective absorber of longwave radiation emitted from the Earth’s surface. (Greenhouse gas) • Its concentration in the atmosphere has increased ~18% since 1958. Ozone (0.01%) • (O3) is an unusual molecule made up of 3 Oxygen atoms. It forms when individual O atoms collide with an O2 molecule and exists in very small concentrations in the stratosphere (we’ll define this a little later). • O3 is vital for absorbing lethal UV radiation from the sun. As it does this, it breaks down into its constituent components O + O2. • Near the surface ozone is a pollutant, but exists there in extremely small amounts. 3. Aerosols • are small solid particles or liquid droplets (except water particles) in the air. • They are formed by both natural and anthropogenic means. Aerosols typically have residence times of a few days to several weeks. • Apart from pollution, aerosols play an important role as condensation nuclei, the core about which water can condense in clouds. • Formed from chemical reactions, wind-generated dust, volcanic ejections, sea spray, and combustion (e.g., fine ash) removed from the atmosphere in precipitation. Composition of the atmosphere - recap 1. Permanent gases Name two permanent gases 2. Variable gases Name two variable gases 3. Aerosols Name two ways aerosols form Vertical Structure of the atmosphere 1. Density 2. Pressure 3. Temperature We’ll start this section on Thursday